tcp: better SYNACK sent timestamp

Detecting spurious SYNACK timeout using timestamp option requires
recording the exact SYNACK skb timestamp. Previously the SYNACK
sent timestamp was stamped slightly earlier before the skb
was transmitted. This patch uses the SYNACK skb transmission
timestamp directly.

Signed-off-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 695f840..30c6a42 100644 (file)
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -6319,7 +6319,7 @@ static void tcp_openreq_init(struct request_sock *req,
        req->cookie_ts = 0;
        tcp_rsk(req)->rcv_isn = TCP_SKB_CB(skb)->seq;
        tcp_rsk(req)->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
-       tcp_rsk(req)->snt_synack = tcp_clock_us();
+       tcp_rsk(req)->snt_synack = 0;
        tcp_rsk(req)->last_oow_ack_time = 0;
        req->mss = rx_opt->mss_clamp;
        req->ts_recent = rx_opt->saw_tstamp ? rx_opt->rcv_tsval : 0;

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 3206192..0c4ed66 100644 (file)
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -3247,7 +3247,11 @@ struct sk_buff *tcp_make_synack(const struct sock *sk, struct dst_entry *dst,
                skb->skb_mstamp_ns = cookie_init_timestamp(req);
        else
 #endif
+       {
                skb->skb_mstamp_ns = tcp_clock_ns();
+               if (!tcp_rsk(req)->snt_synack) /* Timestamp first SYNACK */
+                       tcp_rsk(req)->snt_synack = tcp_skb_timestamp_us(skb);
+       }
 
 #ifdef CONFIG_TCP_MD5SIG
        rcu_read_lock();